In the present paper the use of wide-band spectral analysis to simultaneously investigate fast and slow components of blood pressure (BP) and heart rate (HR) variability is addressed from both a methodological and a practical point of view. After a short review of the technical problems involved in this kind of analysis, the results obtained by the wide-band spectral approach in evaluating the effects of sino-aortic baroreceptor denervation (cats) and aging (humans) on the different components of BP and HR variability are presented. An important finding from use of wide-band spectral analysis is that the power of the BP spectral components tends to be inversely related to the frequency (1/f trend), namely, the slower the BP fluctuation the higher its contribution to the overall BP variance. The occurrence of slow BP fluctuations of pronounced magnitude, however, may appear in apparent contrast with the anti-oscillatory action of the arterial baroreflex. A possible explanation for this paradoxical phenomenon is that also the sensitivity of the baroreflex is modulated in a 1/f fashion. Experimental data supporting this hypothesis are shown.